Method for plasma etching using periodic modulation of gas chemistry

ABSTRACT

A method for etching a layer over a substrate is provided. A gas-modulated cyclic process is performed for more than three cycles. Each cycle comprises performing a protective layer forming phase using first gas chemistry with a deposition gas chemistry, which is performed in about 0.0055 to 7 seconds for each cycle and performing an etching phase for the feature through the etch mask using a second gas chemistry using a reactive etching gas chemistry, which is performed in about 0.005 to 14 seconds for each cycle. The protective layer forming phase comprises providing the deposition gas and forming a plasma from the deposition gas. Each etching phase comprises providing a reactive etching gas and forming a plasma from the reactive etching gas.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of obtaining a structure on asemiconductor wafer by etching through structures defined by a mask,such as a photoresist mask, hard mask, or a stacked mask, using aplasma.

2. Description of the Related Art

In semiconductor plasma etching applications, a plasma etcher is usuallyused to transfer a mask pattern into a circuit and line pattern of adesired thin film and/or filmstack (conductors or dielectric insulators)on a wafer. This is achieved by etching away the films (and filmstacks)underneath the photoresist materials in the opened areas of the maskpattern. This etching reaction may be initiated by the chemically activespecies and electrically charged particles (ions) generated by excitingan electric discharge in a reactant mixture contained in a vacuumenclosure also referred to as a reactor or process chamber.Additionally, the ions may be also accelerated towards the wafermaterials through an electric field created between the gas mixture andthe wafer materials, generating a directional removal of the etchingmaterials along the direction of the ion trajectory in a manner referredto as anisotropic etching. At the finish of the etching sequence, themasking materials are removed by stripping them away, leaving in itsplace a replica of the lateral pattern of the original intended maskpatterns. This etching method is illustrated in FIG.'S 1A-C. In thismethod, a plasma etching process is used to transfer directly thephotoresist mask pattern 104 into that of the underlying oxidedielectric thin film 108, as shown in FIG. 1A. The etching generates acontact hole 112 and erodes and damages the photoresist 104, as shown inFIG. 1B. The photoresist is then removed leaving the contact hole 112 inthe oxide 108, as shown in FIG. 1C. During the etching process, the maskmaterials are usually eroded and/or damaged in exchange for the patterntransfer. Consequently, some of the damage and erosion also may betransferred to the underlying layers leaving such undesirable patterndistortions such as striation, CD enlargement, faceting, etc.

An objective of the etching methodology, therefore, may include reducingthe mask erosion to enhance the fidelity of the pattern transfer fromthe mask patterns. For this purpose, it has been proposed to include apassivation gas in the reactive etching mixture. This passivation gascan be chosen in such a way that its presence selectively reduces theetching damage and erosion of the masking materials relative to theremoval rate of the thin film materials to be etched. The passivationgas can be chosen in such a way that, an etching retardation coating isgenerated on the surface of the masking materials acting as a barrier toslow down the etching reaction. By design, the passivation gas is chosenin a way that it additionally beneficially forms an etching retardationcoating on vertical surfaces of the film structures to be etched, suchthat etching reaction cannot advance in the absence of the ionbombardment. By the nature of the vertical trajectory of the chargedparticles, etching can therefore advance only in the vertical direction,with little to no etching in the lateral direction, creating ananisotropic etching profile. Hence, the presence of a passivation gas inthe etching mixture is very important for the advantage of betteretching mask protection and highly anisotropic etching profile by theuse of relatively high energy directional ion bombardment.

It has already been proposed that the reactive gas mixture containetching gases and polymer formers, with the latter acting the role of apassivation gas. In this case, the etching gases release highly reactivespecies by the excitation of an electrical discharge, which in turnetches the thin film materials to be etched as well as the maskingmaterials by the mechanism of a spontaneous reaction. By the nature ofspontaneous reactions, the etching reaction advances in both thevertical as well as the lateral surfaces, creating isotropic etchingprofiles. The co-presence of a polymer former, through generation of apolymer deposit on the surface of the etching structures and maskingmaterials, can be used to create simultaneously high etching selectivityto masking materials and etching anisotropy, in conjunction with the ionbombardment.

It also has already been proposed that the reactive gas mixture containpolymer former gases and an etching enabler gas. The role of the etchingenabler gas is to enable the etching enabler gas to release highlyreactive species by reacting with the polymer former gases in thepresence of an electrical discharge. Alternatively, a retardationcoating on the etching materials as well as the masking materials canalso be formed by chemical reaction of a properly chosen passivation gasdirectly with the surfaces of these materials.

A common disadvantage of the above mentioned methods is that the optimumconditions for different aspects of the etching requirement usually donot coincide and by mixing the gases some of the unique properties ofeach precursor gases may be lost due to inter-reactions. The etchingcondition optimization almost always involve complex trade-offs into asingle etching condition that may not be the optimum should thedifferent etching chemistries be separate.

A variant of the etching methodology is taught in U.S. Pat. No.5,501,893, issued Mar. 26, 1996 to Laermer et al., entitled “Method ofAnisotropically Etching Silicon”. This method separates out the etchinggases and polymer former gases into two different steps, each consistingpurely of one type of chemicals but not the other. The deposition steptaught in Laermer forms an approximately 50 nm thick Teflon-like polymerlayer during a suggested one minute deposition step. This allows forfast etching rate at low ion bombardment energies, since at low ionbombardment energies, high selectivities to masking materials can beachieved for certain spontaneous etching reactions if the activationenergy is slightly lower for the reaction at the surface of the etchingmaterials than the masking materials.

By removing the polymer former from the etching process, it is believedthat the etching process is isotropic during the duration when theetching is proceeding, since there is no retardation layer to preventthe lateral etching from occurring. Additionally, without thepassivation gas in the etching mixture, it may be difficult to obtainsufficient etching selectivity to the masking materials if the desire isthere to use higher ion energies. Many etching applications can benefitfrom high ion bombardment energy to obtain high aspect ratio structuresin very small dimension structures, for example. It is also believedthat such processes have undesirable striation and faceting.

Additional proposed methods include a stacked masking scheme to improvethe overall etching resistance of the masking materials. This isillustrated in FIG.'S 2A-F. In FIG. 2A an oxide layer 204 is provided.FIG. 2B shows a hardmask layer 208 placed over the oxide layer. Aphotoresist mask 212 is placed over the hardmask layer 208, as shown inFIG. 2C. The photoresist mask 212 is used to pattern the hardmask layer208 to create a patterned hardmask layer 214, and the photoresist layer212 may be removed, as shown in FIG. 2D. A contact hole 216 is etched inthe oxide layer 204, using the patterned hardmask layer 214 as a mask asshown in FIG. 2E. The hardmask is then removed leaving the contact 216in the oxide layer 204, as shown in FIG. 2F.

The advantages of this method are that, by having a more inert hardmaskfrom which to transfer patterns (circuits and lines) to the underlyingfilms, the etch performance is much enhanced and the requirement on theetching and photolithography is also much reduced. The disadvantages ofthis method are that, by introducing new process steps and new tool setsinto the process flow, it is of higher cost and lower overallthroughput. In addition, the extra process complexity also introducesdifficulties by itself. For example, the Si hardmask used for dielectriccontact etch applications is not as easily stripped as the photoresistmask.

SUMMARY OF THE INVENTION

To achieve the foregoing and in accordance with the purpose of thepresent invention, a method for etching a feature in a layer through anetch mask over a substrate is provided. A gas-modulated cyclic processis performed for more than three cycles. Each cycle comprises performinga protective layer forming phase using first gas chemistry with adeposition gas chemistry, wherein the protective layer forming phase isperformed in about 0.0055 to 7 seconds for each cycle. The protectivelayer forming phase comprises providing the deposition gas and forming aplasma from the deposition gas. Each cycle further comprises performingan etching phase for etching the feature through the etch mask using asecond gas chemistry using a reactive etching gas chemistry, where thefirst gas chemistry is different than the second gas chemistry, whereinthe etching phase is performed in about 0.005 to 14 seconds for eachcycle. Each etching phase comprises providing a reactive etching gas andforming a plasma from the reactive etching gas.

In another embodiment an apparatus for etching a feature in a layerthrough an etch mask over a substrate is provided. A process chamber,within which the substrate may be placed is provided. A first gaschemistry source for providing first gas chemistry of a deposition gaschemistry is provided. A second gas chemistry source for providing asecond gas chemistry of a reactive etching gas chemistry is provided. Acontroller controllably connected to the first gas chemistry source andthe second gas chemistry source, where the controller comprises computerreadable media for performing a gas-modulated cyclic process for morethan three cycles is provided. The computer readable media comprisescomputer instructions for performing a protective layer forming phaseusing the first gas chemistry with the deposition gas chemistry, whereinthe protective layer forming phase is performed in about 0.0055 to 7seconds for each cycle, comprising, computer instructions for providingthe deposition gas and computer instructions for forming a plasma fromthe deposition gas. The computer readable media further comprisescomputer instructions for performing an etching phase for etching thefeature through the etch mask using the second gas chemistry using areactive etching gas chemistry, where the first gas chemistry isdifferent than the second gas chemistry, where the etching phase isperformed in about 0.005 to 14 seconds for each cycle, comprisingcomputer instructions for providing the reactive etching gas andcomputer instructions for forming a plasma from the reactive etchinggas.

In another embodiment of the present invention, a method for etching afeature in a layer through an etch mask over a substrate is provided. Agas-modulated cyclic process is performed for more than three cycles.Each cycle comprises performing a first etching phase, wherein the firstetching phase is performed in about 0.0055 to 14 seconds for each cycle.The first etching phase comprises providing a first etch gas and forminga plasma from the first etch gas. Each cycle further comprisesperforming a second etching phase, wherein the second etching phase isperformed in about 0.005 to 14 seconds for each cycle. Each secondetching phase comprises providing a second etch gas that is differentthan the first etch gas and forming a plasma from the second etch gas.

These and other features of the present invention will be described inmore details below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG.'S 1A-C are schematic views of the formation of a contact holefeature through a prior art process.

FIG.'S 2A-F are schematic views of the formation of a contact holefeature through another prior art process.

FIG. 3 is a flow chart of an embodiment of the invention.

FIG.'S 4A-F are schematic views of the formation of a contact hole usingthe inventive process.

FIG. 5 is a schematic view of a system that may be used in practicingthe invention.

FIG. 6 is a scanning electron micrograph of a top view of results ofetching a dense array of contacts using an example of the invention.

FIG. 7 is a scanning electron micrograph of a profile view of results ofetching a dense array of contacts using an example of the invention.

FIG.'S 8A-E schematically illustrate the build up of material on asurface in an inventive regime of fast cycling using submonolayers.

FIG.'S. 9A-D schematically illustrate the build up of material on asurface in the regime of slower cycling.

FIG.'S 10A and 10B illustrate a computer system, which is suitable forimplementing a controller used in embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

It is believed that forming protective layers, such as sidewallpassivation layers that are on the order of 10 nm thick or greater andthen etching, while using the protective layers as a passivation layer,may cause striations and faceting. Without being bound by theory, it isbelieved that layers of such thickness are not sufficiently conformal toprovide desired protection against striation. It is believed that thethin protective layers provided by the invention significantly reducestriation. Such a thin protective layer may also reduce faceting. It isalso believed that this reduces CD enlargement, providing CD control orcontrol of CD bias, where CD bias is defined as CD change during etch.

The invention is a new etching method in which an in-situ gas-modulatedcyclic etch process alternates between a protective layer formationphase and an etch phase to enhance the overall etch performance withoutunduly sacrificing simplicity and cost-effectiveness. The modulationspecifically includes cyclic variation of the composition and/or flowratios of the process feed gases, and may also include synchronizedvariations in the RF power, gas pressure, and temperatures. The cyclicprocess is characterized by a total cycle time and by the cycle timeratio, which is the ratio between time for the protective layerformation phase and the time for the etch phase.

U.S. patent application Ser. No. 10/295,601, entitled “METHOD FOR PLASMAETCHING PERFORMANCE ENHANCEMENT, by Huang et al., filed on Nov. 14, 2002and incorporated by reference for all purposes, discloses that anin-situ plasma process may be used to enhance and/or repair the maskand/or the vertical sidewalls of etching features, during the etchingprogression. In such a process, a plasma chemical process step isinitiated for a short duration before and/or after the wafer is exposedto an etching plasma for a desired duration.

In the present invention, this approach is modified such that theprocess step responsible for protecting the mask and sidewalls isintroduced as one phase of a gas-modulated cyclic process, inalternation with a compatible etch phase.

The protective layer formation process may be chosen in such a way thata thin film of material is formed on the surfaces of the mask and/or thesidewalls of the film being etched to prevent etch erosion, faceting,and striation. This thin coating may be of a material that is compatiblewith later stripping process for ease of final removal but more etchresistant than the mask materials. For example, a carbon-rich thin film,containing very low to no amount of other elements, may be used to coata photoresist mask so that protected mask features are not easily erodedby the subsequent etching process. In other words, it may change thesurface composition of the mask pattern such that the mask behaves likea pseudo hardmask, having certain beneficial etching characteristics ofan amorphous carbon hardmask. Alternatively, the layer forming processmay also be used in such a way that the formation of the thin coating onthe mask pattern largely compensates for and/or repairs the maskpatterns damaged/eroded by the prior etch process. The relativeinertness of the coating to the subsequent etching reaction isbeneficial so as to not to alter the fine balance obtained in theetching step. Alternatively the thin coating may be produced usingprocess conditions which provide a smooth conformal coverage ofsidewalls, preventing the initiation of striations due to rough and/orcorrugated sidewall polymer coatings.

The etching gas mixture may contain etchant species and a passivationspecies so as to not lose the benefits associated with a passivation gasin the etching chemistry. The ratio of the etching to passivationcomponents, along with a plurality of other processing conditions, isfinely balanced to achieve optimum processing results, such asphotoresist selectivity, etching anisotropy and etching rate etc. Theelectrical discharge power may be kept high and the energy of thecharged particles is also kept high to obtain high etch rate and goodetching anisotropy in small dimensional structures. The protective layerformation and etching cycle is repeated a large number of times untilthe completion of the etching task.

To facilitate understanding, FIG. 3 is a flow chart of an embodiment ofthe invention. A mask is provided on a layer to be etched (step 304).The mask may be a photoresist mask, a hard mask, or a stacked mask.FIG.'S 4A-F are schematic illustrations of the process. FIG. 4A shows aphotoresist mask 404, which has been provided on an oxide layer 408 tobe etched, which is on a substrate. The substrate is placed in a processchamber (step 306).

FIG. 5 is a schematic view of a process chamber 500 that may be used inthe preferred embodiment of the invention. In this embodiment, theplasma processing chamber 500 comprises confinement rings 502, an upperelectrode 504, a lower electrode 508, a gas source 510, and an exhaustpump 520. The gas source 510 comprises a protective layer gas source512, an etchant gas source 514, and an additional gas source 516. Withinplasma processing chamber 500, the substrate wafer 580, over which theoxide layer is deposited, is positioned upon the lower electrode 508.The lower electrode 508 incorporates a suitable substrate chuckingmechanism (e.g., electrostatic, mechanical clamping, or the like) forholding the substrate wafer 580. The reactor top 528 incorporates theupper electrode 504 disposed immediately opposite the lower electrode508. The upper electrode 504, lower electrode 508, and confinement rings502 define the confined plasma volume 540. Gas is supplied to theconfined plasma volume by gas source 510 through a gas inlet 543 and isexhausted from the confined plasma volume through the confinement rings502 and an exhaust port by the exhaust pump 520. The exhaust pump 520forms a gas outlet for the plasma processing chamber. An RF source 548is electrically connected to the lower electrode 508. Chamber walls 552define a plasma enclosure in which the confinement rings 502, the upperelectrode 504, and the lower electrode 508 are disposed. The RF source548 may comprise a 27 MHz power source and a 2 MHz power source.Different combinations of connecting RF power to the electrodes arepossible.

An 2300 Exelan™ dielectric etch system made by Lam Research Corporation™of Fremont, Calif. modified to provided the cycle time required by theinvention may be used in a preferred embodiment of the invention. Acontroller 535 is controllably connected to the RF source 548, theexhaust pump 520, a first control valve 537 connected to the depositiongas source 512, a second control valve 539 connected to the etch gassource 514, and a third control valve 541 connected to the additionalgas source 516. A showerhead may be connected to the gas inlet 543. Thegas inlet 543 may be a single inlet for each gas source or a differentinlet for each gas source or a plurality of inlets for each gas sourceor other possible combinations.

The structure is then prepared for a modulated etch (step 308). Suchpreparation may comprise steps such as opening a BARC layer.

A gas-modulated cyclic etch process is then carried out (step 312).During the gas-modulated cyclic etch process, the process chamber 500modulates between at least two phases. One phase is a step optimized toform a protective layer (step 316). The other phase is a step optimizedfor etching (step 326). The alternation between these phases is achievedby synchronized modulation of gas flow rates, and possibly RF power,surface temperature, and gas pressure. In the preferred embodiment, atotal cycle time is not greater than about 21 seconds. More preferably,a total cycle time is performed in 0.01 to 10 seconds. Most preferably,a total cycle time is performed in 0.5 to 5 seconds. Preferably, thecycle time ratio (protection: etch) is between 0.01 and 20. Morepreferably, the cycle time ratio (protection: etch) is between 0.05 and5. Most preferably, the cycle time ratio (protection: etch) is between0.2 and 1. Preferably, the gas modulation is carried out for betweenabout 3 to 50,000 cycles. More preferably, the gas modulation is carriedout for about 20 to 1000 cycles. Most preferably, the gas modulation iscarried out at least about 100 cycles.

During a phase optimized to form a protective layer (step 316), aprotective layer is deposited on side walls of the etched features andpossibly on top of the etch mask. The deposition may be asymmetric sothat the amount of deposition is formed preferentially more on themasking material than on the sidewalls. This may be aided by theline-of-sight of the location to the deposition source as well as by theselective nature of the chosen deposition process. In other words, thedeposition chemistry may be chosen in such a way that a coating isformed preferentially on the masking materials due to differences in thechemical reactivity of the materials. As can be seen in FIG. 4B athicker protective layer 412 is formed on the top of the photoresistmask 404 than on the exposed oxide surface at the bottom of thephotoresist mask and on the sidewalls of the photoresist mask. It shouldbe noted that other dimensional relationships of the drawings may notnecessarily be to scale. For example, the thickness of the protectivelayers compared to the thickness of the mask and etched layer, may notbe to scale, but such protective layers may be drawn thicker forclarity. In the preferred embodiment, the deposition is done in-situ inan etch chamber using a plasma enhanced chemical vapor deposition (CVD)process, which deposits a thin protective layer on the sidewall of thephotoresist. The deposition process may apply some ion bombardmentenergy to allow for selectivity of such deposition. In such a processthe thickness of the sidewalls may be about two thirds the thickness ofthe layer on top of the mask.

In other embodiments, the processing conditions may be changed as theetch front progresses through the material being etched to vary thethickness and spatial distribution of the protective layer. For example,it may be desirable to form a thicker coating on the sidewall of thefilm being etched as the etching proceeds deeper in order to protect thesidewalls from further distortion by the subsequent etching. A variationof cyclic processing conditions as the etch proceeds may provide forthis. Since the layer forming and etching are separate phases of thecycle, the process conditions for the layer forming phase may beoptimized for this result without interfering with the etch phase.Alternatively the total cycle time and/or cycle time ratio may beadjusted as the etch proceeds to provide this variation, without anychange to the process parameters for the individual phases. In anotherpreferred embodiment, the protective layer may be only deposited on thesidewalls.

During the protective layer formation phase, the fluorine-to-carbonratio of the deposition gas is not greater than 2:1. Examples ofdeposition chemistries that may be used for plasma enhanced CVD may be,but are not limited to, CH₃F, CH₂F₂, C₂H₅F, C₃H₇F, C₂H₃F, CH₄, C₂H₄,C₂H₆, C₂H₂, C₃H₈, and SiH₄, Si(CH₃)₄, Si(C₂H₅)₄. It is preferred thatthese chemicals are halogen free or have a halogen to carbon ratio of nogreater than 2:1. Without being limited by theory, it is believed thatthe carbon based chemistry forms a thin etch resistant amorphous carbonlayer. The silane SiH₄ would be used to form an amorphous silicon layer(or polycrystalline silicon layer) over the photoresist. In addition,the protective layer may have been modified with the presence of some Fand H components. The presence of other elements, such as F, may be usedto yield selective activity on different material surfaces such thatdeposition occurs preferentially on one but not the other materials,such as on the photoresist mask materials but not on SiO₂ layer, underappropriate ion bombardment. Other methods, such as sputtering, may beused to form the protective layer.

To accomplish the gas-modulated cyclic processing, synchronized controlof the etch system parameters may be implemented as follows. To initiatethe protective layer formation phase at the start of a cycle, thecontroller 535 may cause the first valve 537 to allow a deposition gasfrom the deposition gas source 512 into the process chamber 500, whilecausing the second valve 539 to prevent etching gas from the etchant gassource 514 from entering the process chamber. The controller 535 mayalso control the power supplied by the RF source 548 and the exhaustpump 520 in synchronization with the valve controls. The controller mayalso be used to control the gas pressure in the wafer area, waferbackside He cooling pressure, the bias on the substrate, and varioustemperatures in synchronization with the valve controls. Table I is atable of some of the parameters that may be used in a protective layerformation phase of a cyclic process in the preferred embodiment of theinvention. TABLE I More Preferred Most Preferred Preferred Range RangeRange Bias Voltage >50 volts >100 volts >300 volts Bias Energy >50eV >100 eV >300 eVThe bias may be provided by placing a constant voltage between an upperelectrode above the substrate and a lower electrode below the substrate.In the preferred embodiment, an electrical negativity can be formed onthe substrate holding the wafer materials (thereby applying a bias tothe wafer) by applying a radio frequency (RF) voltage supplied by an RFpower generator. This has the effect of drawing the positively chargedparticles towards the electrically biased substrate at an energydetermined by the electrical negativity controlled by the amplitude ofthe RF voltage. It is, therefore, possible to supply and vary the ionbombardment energy by controlling the RF power (and hence the RFvoltage) applied to the substrate holder.

The protective layer formation phase 316 is an independent phase in thecyclic etch process 312 which may include different combinations ofdeposition gases as required for different etching applications ofdifferent materials, where the deposition may provide a protectivecoating around the etching features including the masking features.Preferably, the time of the cycle devoted to this phase is about 0.005to 7 seconds. More preferably, the time of the cycle devoted to thisphase is about 0.05 to 5 seconds. Most preferably, the time of the cycledevoted to this phase is about 0.25 to 2.5 seconds. Preferably, a layerwith a thickness of less than 100 Å is formed on the top and/orsidewalls over the duration of a single protective layer formationphase. More preferably, a layer between about 0.1 and 50 Å is formed onthe top and/or sidewalls over the duration of a single protective layerformation phase. Most preferably, a layer between about 1 and 10 Å isformed on the top and/or sidewalls over the duration of a singleprotective layer formation phase. In the case of less than about 10 Ålayer thickness, the coverage may more accurately be described as afraction of a monolayer in one embodiment, the protective layer forms asingle monolayer over the duration of a single protective layerformation phase. In another embodiment, the protective layer forms asub-monolayer, which is a layer that does not completely cover thesurface with a single atomic or molecular layer but instead may providea certain percentage (i.e. 75%) of surface coverage, over the durationof a single protective layer formation phase.

The etch phase 320 is an independent phase in the cyclic etch process312 which is performed to advance the etch front 460, producing the etchfeature 416 (step 320), as shown in FIG. 4C. Etching applications mayinclude, but are not limited to, a dielectric contact etch, includinghigh aspect ratio contact (HARC), damascene etch, dielectric trench etch(shallow or deep), self-aligned contact etch, gate mask open etch, viadielectric etch, dual-damascene via etch, dual damascene trench etch,conductor gate etch, conductor deep trench etch, conductor shallowtrench isolation etch, and hardmask opening.

Preferably, the etch phase uses a high ion energy to provide adirectional etch. The etch phase may remove some or all of theprotective layer 412, as shown, over the duration of a single etchphase. All of the protective layer on some of the surfaces may beremoved over the duration of a single etch phase. In this example, theprotective layer forming the sidewall on the photoresist 404 and at thebottom of the feature has been removed. Other parts of the protectivelayer may only be partially removed. In this example, only part of theprotective layer 412 on the top surface of the photoresist 404 has beenremoved. In other embodiments, other parts of the protective layer maybe partially etched way or completely etched away. The etch phaseremoves some of the layer to be etched, and advances the etch front 460.

To provide the etch phase of the cycle, the controller 535 may cause thesecond valve 539 to allow etching gas from the etchant gas source 514into the process chamber 500, while causing the first valve 537 toprevent deposition gas from the deposition gas source 512 from enteringthe process chamber. The controller 535 may also control the powersupplied by the RF source 548 and the exhaust pump 520 insynchronization with the valve controls. The controller may also be usedto control the gas pressure in the wafer area, wafer backside He coolingpressure, the bias on the substrate, and various temperatures insynchronization with the valve controls. The cycle continues byreturning to the protective layer formation phase described above, andby repeating the alternation between phases of the cycle for as long asthe cyclic etch process is required. The controller 535 may cause thethird valve 541 to allow common gases from the common gas source 516 toenter the process chamber during both phases of the cycles, if there isa common gas or mixture of gases which is desired in both the protectivelayer formation phase and the etch phase of the cycle.

Since the etch phase of the cyclic process uses high energy ions toprovide a directional etch, a polymer former gas may be provided duringthe etch phase. The polymer former gases may be, for example,hydrocarbons, fluorocarbons, and hydrofluorocarbons, such as C₄F₆, C₄F₈,CH₃F, CH₂F₂, CH₄, C₃F₆, C₃F₈, and CHF₃. These polymer former gases wouldform a polymer layer that is continuously deposited and etched duringthe etch phase.

Table II is a table of some of the parameters that may be used in anetch phase of a cyclic process in the preferred embodiment of theinvention. TABLE II More Preferred Most Preferred Preferred Range RangeRange Bias Voltage >200 volts >300 volts >400 volts Bias Energy >200eV >300 eV >400 eV

Preferably, the time of the cycle devoted to this phase is about 0.005to 14 seconds. More preferably, the time of the cycle devoted to thisphase is about 0.05 to 7 seconds. Most preferably, the time of the cycledevoted to this phase is about 0.25 to 2.5 seconds. Preferably the depthof the etch increases by less than 500 Å over the duration of a singleetch phase. More preferably, the depth of the etch increases by betweenabout 5 and 250 Å over the duration of a single etch phase. Mostpreferably, the depth of the etch increases by between about 10 and 50 Åover the duration of a single etch phase. In the case of a change inetch depth of less than about 10 Å in a single etch phase, this changemay more accurately be described as a fraction of a monolayer ofmaterial removed during a single etch phase. In one embodiment, theamount of material removed over the duration of a single etch phase isabout one monolayer. In another embodiment, the amount of materialremoved over the duration of a single etch phase is a less than onemonolayer.

The depth of the feature in the figures may not be according to scale.For example, the depth of the etch may be shown much greater than theactual etch depth, since the small etching changes per cycle may bedifficult to illustrate.

The cyclic process is repeated over many cycles. An additionalprotective layer 418 is deposited on the photoresist mask, as shown inFIG. 4D. In this example, the remaining part of the old protective layerbecomes part of the new protective layer 418. The feature is thenfurther etched through the photoresist mask (step 312), providing adeeper contact hole 416, as shown in FIG. 4E. Preferably, thisgas-modulated cycle or loop of providing alternating deposition andetching phases is repeated more than 3 times. More preferably, thiscycle is repeated more than 20 times. Most preferably, this cycle isrepeated at least 100 times.

When no further etching is desired, the gas-modulated cyclic process(step 312) is complete. In the last cycle, the etching phase maycompletely etch away the protective layer, as shown in FIG. 4E. However,a subsequent processing step after the cyclic etch process may also beused to remove the protective layer and/or complete the etch of theoxide layer 408. Further process steps, such as stripping thephotoresist mask may be performed to yield the oxide layer 408 with acontact hole 416, as shown in FIG. 4F. The photoresist mask may bestripped in the process chamber 500 or after removal from the processchamber 500. Further process steps may also be required to remove a filmat the bottom of the contact hole.

In an alternative embodiment, the gas-modulated cyclic process may beterminated before the oxide etch is completed, allowing theincorporation of a conventional etch step to complete the etch. This maybe desirable as a means of controlling selectivity to the stop layerunderlying the oxide layer.

Examples of materials for the photoresist mask may include, but are notlimited to the newer generation of photoresists, such as, deep UVphotoresist, 193 nm photoresist, 157 nm photoresist, EUV photoresist,e-beam photoresist, and x-ray photoresist. The older generation ofphotoresist polymer materials are designed to contained unsaturated C—Cbonds, such as the C—C double bond and phenolic groups to provide therequired high etching resistance, namely, chemical inertness to theetching gas mixture. These bonds are strong and require a highactivation energy to break and therefore, at relatively low ionenergies, the older generation photoresist can show remarkably lowetching rate to the etching gas mixture. The newer generation ofphotoresist, including 193 nm and 157 nm, may not contain theseunsaturated bonds because these unsaturated bonds absorb at thelithography exposure wavelength. The absence of these unsaturated bondsleads to much reduced photoresist etching resistance. By providingprotective coatings on the photoresist during the cyclic process etch,the etching resistance of the photoresist is much improved, even at highion bombardment energy. The high ion bombardment energies at which theinvention may improve etching resistance of the photo resist may be50-2,000 eV. More preferably the ion bombardment energy may be 200-1,500eV. Most preferably, the ion bombardment energy is 500-1,000 eV.

Without being bound by theory, it is believed that cyclic processingprovides a different processing regime, because the properties ofextremely thin films, deposited and etched in short timescales, aredifferent from the properties of thicker films. Using the gas-modulatedcyclic processing approach, with short cycle times, an extremely thinprotective layer is deposited, such as a sidewall film or film on thetop photoresist surface. This film and the oxide film are subsequentlyetched in very small amounts during the next phase of the cycle. Thethin protective layer thickness may be in the monolayer range (i.e.sub-monolayers, monolayers, or layers of a few atoms or molecules).

The production of thin protective layers in the monolayer range isdependent on the deposition rate times the deposition time. Variousdeposition rate and deposition time combinations may be used to providea thin protective layer in the monolayer range. For example, adeposition that provides a sidewall deposition rate of approximately 1nm/sec and a top surface deposition rate of approximately 2 nm/secprovides a monolayer range thin protective layer with an approximately0.5 nm thickness, when the deposition step is for 0.25-0.5 seconds percycle. (i.e. a 1 nm/sec deposition rate×0.5 seconds=0.5 nm deposition.).The same monolayer range may be achieved by increasing the depositionrate and decreasing the cycle time or by decreasing the deposition rateand increasing the cycle time. This flexibility provides additionalcontrol variables.

Without being bound by theory, it is further believed that as thethickness of the protective film approaches the dimensions of theconstituent molecules, e.g. approaching monolayer coverage, the film mayadopt chemical and physical properties which are distinct from bulkproperties of the protective film. In this regime the concept of a thinfilm may no longer be applicable and it may be more accurate to considerthe mixture of chemical species present in the surface and near-surfaceregion of the material. Such species may be present as loosely boundphysisorbed species, as more tightly bound chemisorbed species, or asparts of larger structures, e.g. polymer molecules, glasses, or bulkcrystals. These surface and near-surface species will include protectivespecies deposited during the protective layer phase of cyclicprocessing, but may also include species deposited or evolved during theetch phase of the cyclic process, as well as other species from theoriginal substrate or arising from chemical reactions between thevarious species. The unique properties in the approximate monolayerregime may result from the interaction of these different surface andnear-surface species with each other and with the substrate material.These interactions would be suppressed in the case of a thickerprotective film, which would cover the substrate with several monolayersor more in each protective layer phase, and therefore expose only thesurface of the protective material by the time the next etch phasebegins.

Without being bound by theory, it is further believed that in theextreme where surfaces are receiving limited flux within each cycle,corresponding to submonolayer coverage during each individual protectionand etch phase, a truly novel process regime is achieved. In this case,the concept of alternating process steps becomes inaccurate at amicroscopic scale, even though it is actually being used to control theprocess. At a microscopic scale, the surface reactions will proceedbased on the arrival and departure of species and the chemical reactionsof these species. Reactions occur continually but are punctuated by theoccasional impact of an energetic species, such as an ion, which candrive hyper-thermal reactions. Most of the critical reactions occurduring these brief instants of excitation. In the submonolayer regime ofcycling, the surface sees a quasi-steady state where the flux ofreactants reaching the surface is essentially an average of the twodifferent plasma conditions, with reactions occurring between themixture of these species.

It is believed that this is a fundamentally different regime fromtraditional, single-step, steady state etching, because the mixture ofspecies reaching the surface is produced from two distinct plasmaconditions. If the process conditions of the phases of the gas-modulatedcyclic process were combined into a single steady-state recipe step, theresulting time-averaged flux of species reaching the surface would bemodified due to the interaction of the different gases in the plasma. Itis believed that by separating the plasma conditions in time withgas-modulated cyclic processing, the overall mixture of species reachingthe surface can be controlled to an unprecedented degree. Conditions forthe two different phases of the cycle can be very different, due to theability to modulate the gas chemistry. As a result, very differentchemical species can be produced in the different phases of the cycle,to achieve a mixture which might be impossible with a single-stepsteady-state process. This mixture is the linear combination of fluencesfrom the two discrete plasma conditions produced by the alternatingphases of the cycle. The ratio of these fluences is controlled by thecycle time ratio. The cycle time ratio therefore becomes an additionalprocess control variable.

The gas-modulated cyclic processing approach is able to provide a regimeof near-monolayer and sub-monolayer coverage (monolayer range) that isaccessible in the short cycle time regime. By increasing the cycle timesufficiently, the regime of bulk protective layers, with thicknesses ofmany monolayers, alternating with sustained etch conditions, may also beaccessed. Between these two extremes of cycle time, a continuum ofbehavior may be accessed, to allow the balancing of desirable andundesirable results characteristic to the two extremes of the approach.Therefore, the inventive gas-modulated cyclic processing provides theflexibility to provide all of these regimes in this continuum. The totalcycle time therefore becomes an additional process control variable.

FIG.'S 8A-E schematically illustrate the build up of material on asurface in the regime of fast cycling using submonolayers. In thisexample, each phase of the cyclic process is adding species to thesurface sites, but different species are produced in the differentphases. This is indicated by the alternation between black and whitecircles above the surface for the different phases. These circlesrepresent depositor molecules in the gas phase and on the surface. InFIG. 8A, an initial sidewall surface 804 is shown with surface sites 806unoccupied. FIG. 8B shows the effect of the first phase of the cyclicprocess, where a first species 808 of depositor molecules produced bythe plasma conditions of the first phase are deposited on surface sites806 of the surface 804. Note that not all surface sites 806 are occupiedduring the first application of the first phase. FIG. 8C shows theeffect of the second phase, where a second species 812 depositormolecules produced by the plasma conditions of the second phase, whichare different from the first species 808 of depositor molecules of thefirst phase due to the modulation of gas chemistry and possibly otherprocess parameters. Less than one monolayer is added to the surfacecoverage in this application of the second phase. FIG. 8D shows theeffect of the next application of the first phase of the cyclic process.In this application, monolayer coverage is completed and a second layerbegins to form. FIG. 8E shows the result after several cycles, which isa mixed film with each layer composed of the different species 808, 812produced in the first and second phases.

FIG.'S. 9A-D schematically illustrate the build up of material on asurface in the regime of slower cycling. This is achieved by the sameconditions of the example in FIG.'S 8A-E, with only the total cycle timeincreased by roughly a factor of ten. In FIG. 9A an initial surface 904is shown with surface sites 906 unoccupied. FIG. 9B shows the effect ofthe first phase of the cyclic process, where a first species 908 ofdepositor molecules produced by the plasma conditions of the first phaseare deposited on surface sites 906 of the sidewall surface 904. In thiscase, several monolayers of surface coverage are added during the firstapplication of the first phase. FIG. 9C shows the effect of the secondphase of the cyclic process, where a second species 912 of depositormolecules produced by plasma conditions of the second phase aredeposited on the layer formed by the first species 908 of depositormolecules. Several monolayers of surface coverage are added during thefirst application of the second phase. FIG. 9D shows the result afterone-and-one-half cycle, where is an alternating stack of two differentfilms, with multilayer film composed of layers of the first species 908and the second species 912, each produced during a single phase of thecyclic process.

These examples are presented to show the qualitatively differentmicroscopic results which may be achieved as the total cycle timebecomes comparable to the time required to deposit a single monolayer ofthe surface. It is believed that the different surface films produced inthese two examples may correspond to different process results on thewafer structures, based solely on the variation of total cycle time.This is a simple example, with deposition as the only surface mechanism,but similar arguments could be applied to a more complex combination ofsurface mechanisms. For example, a surface which is alternately exposedto depositor and etchant species by the alternating phases of the cyclicprocess could also exhibit modified behavior when the total cycle timebecomes comparable to the time required to deposit or etch a singlemonolayer of the surface.

As discussed above, it is believed that by using alternating protectiveand etching steps, striation and faceting may be reduced and better etchcontrol may be provided. Without being bound by theory, it is believedthat the regime of near-monolayer and sub-monolayer protective coveragewhich is accessible through gas-modulated cyclic processing and theprotective capabilities of the alternating approach may be controlledand modified to provide unique properties that may help to reducestriation and faceting and provide better etch control.

The layer to be etched may be a dielectric layer (such as siliconoxide), a conductive layer (such as metal and silicon or other type ofsemiconductors), a hardmask layer (such as silicon nitride and siliconoxynitride), or a barrier layer (such as silicon nitride or siliconcarbide). For etching a conductor layer, halogens, such as chlorine,fluorine, or bromine, may be used in the etching step, where thedeposition may contain chemicals used to deposit a carbon-rich thin filmor a thin film containing Si. Preferably, the layer to be etched is adielectric material such as silicon oxide, doped silicate glass, or alow-k dielectric film such as organosilicate glass or SiLK.

The gas-modulated cyclic processing step may be carried out by using thesame carrier gas flow for both forming the protective layer and etching,while reactants for forming the protective layer and reactants foretching are alternately provided. In addition, the RF power,temperature, and/or pressure may be pulsed in synchronization with thegas flows to provide optimal conditions for each phase in thegas-modulated cyclic process.

In another embodiment the entire gas mixture of carrier gases andreactants are alternated. Again, the RF power, temperature, and/orpressure may be pulsed in synchronization with the gas flows to provideoptimal conditions for each phase in the cyclic process. In anotherembodiment, the same gases may be used for both phases, but the relativeflow ratios are changed for each phase. Therefore, to provide adifferent gas chemistry between two different phases of thegas-modulated cyclic process, one could use two entirely differentgases, or use the same carrier gas and different active gases, or usethe same gases with different relative flows.

In an example of different gas chemistries using the same carrier gasflow for both forming the protective layer and etching, the etchant gasfrom the etching gas source is not provided to the plasma processingchamber during the protective layer formation phase. This may be done bynot providing a component of the etching gas or deposition gas. Forexample, oxygen or an oxygen containing gas is a key etching componentto an etching gas. Even though C₄F₆ is also used in the etchant gas,etching cannot be accomplished by C₄F₆ without oxygen in this example.Therefore, by not providing oxygen or an oxygen containing gas duringthe protective layer formation phase is a method of not providing theetching gas during the protective layer formation phase, even if C₄F₆ isprovided during the formation of the protective layer. It is alsopreferred that the formation of the protective layer process is anon-etching or negligently etching at most (comprising less than 10% ofthe layer to be etched) for forming the protective coating. Such adeposition process may be, but is not limited to, plasma enhanced CVDdeposition or sputtering, since CVD and sputtering are not used foretching. If the deposition gas is the same as the polymer former in theetch phase, then the deposition gas may be provided during the etchphase. In addition, bias power during the etch phase may be higher toprovide the directional etching.

Providing a separate deposition phase and the presence of the polymerformer to provide polymerization during the etch phase allows the use ofhigher energy etching ions for higher etching rate and betteranisotropic etching. By keeping passivation gases in an etch phasemixture, it is possible to use higher ion energies without unacceptableerosion and damage of the etching mask. Additionally, anisotropicetching can be achieved during the duration of the etching phase. Byusing cyclic process with alternating protective layer forming phasesand etch phases, mask protection can be optimized. This approach avoidsinter-reactions of etching and retardation gases in the discharge. Forexample, a deposition chemical mixture may be chosen that forms a harderand more durable coating than produced by an etching mixture.Additionally, the deposition chemistry conditions, such as pressure andconcentration, may be tailored to optimize the properties of theprotective layer formation such as the composition and thickness.

It may be desirable that some of the components of the deposition gasare not mixed with components of the etch gas, since some mixingdecreases the efficiency of having separate deposition and etch phases.As a result, the controller in such cases would synchronize themodulated gas flows so that one gas is depleted before another gas isadded.

By having independent protective layer formation and etch-passivationphases, the processing conditions, such as temperature, power, pressure,ion energy, and processing gases, may be independently controlled variedto provide optimal conditions for each phase.

Argon or other inert gases may be used as carrier gases during both theetching and protective layer formation. An example of another inert gaswould be neon.

In an embodiment of the invention, the chamber wall areas, which maycontact the plasma (a mixture of chemicals and charged particlessustained by the electrical discharge), are made to be as small aspossible and to be maintained at elevated temperatures. The object ofthis is to avoid the so-called chamber “memory” effect, by which thechemical elements contained in the coating of the chamber wall areasformed in one processing step can be released to interfere with thesubsequent steps. By minimizing the total deposition on the chamber wallareas, this effect can be reduced, avoiding an interaction between thetwo different phases which may degrade the performance.

It may also be desirable that the gas travel time from the precursorsource to the processing chamber is made to be very short. The gas flowstability time, denoting the time to establish a constant desired flowand the time to establish complete absence of the said gas at theprocessing chamber, is made to be very short so that the transition fromone stable gas mixture composition to the next can be made to be veryfast. The object of this is to avoid inter-mixing of chemicals betweentwo different phases, which may degrade the performance.

It may also be desirable that the electrical system and the controlnetwork controlling the conversion of the electrical power into anelectrical discharge reacts very fast with respect to the changes of thedischarge conditions and power requirements. Furthermore, it maydesirable to be able to quickly change and stabilize other externalconditions of the processing chamber, such as the pressure of the gasmixture and the temperature of the wafer substrate. Allowing suchprocess conditions to be changed quickly allows for a shorter totalcycle time and allows the process conditions to be varied significantlybetween phases to optimize each phases individually. Therefore, it mayalso be desirable to have a computerized system that is able to controland synchronize the rapid modulation of the processing conditions. Thecomputer system is used to send commands for the required periodicchanges and to synchronize these commands using pre-determined timedelays for the various devices providing the plurality of conditionchanges in the processing chamber.

Other embodiments of the invention may provide one or more additionalphases to the cyclic process. For example, a gas-modulated cyclicprocess may have six phases, such as three deposition phases and threeetching phases in a single cycle. The addition of additional phases maybe limited by the increased complexity of each cycle.

Another embodiment may eliminate the use of a polymer providing gasduring the etch phase. Another embodiment of the invention may providetwo etch phases, instead of a deposition phase and etch phase. In suchan embodiment, one etch phase may be an etch process condition thatyields a tapered profiled, while a second etch phase may be an etchprocess condition that yields a bowed profile. In the regime of shortcycle times, each phase of the cycle might modify less than one, roughlyone, or a few monolayers of the surface being etched. In this case thealternation between two different etch phases would produce refinedprocess control capability. Again the gas-modulated cyclic approachprovides the capability to deliver a mixture of species to the surfacewhich could not be produced by a single-step steady-state condition. Andthe ratio between species produced in each phase is easily controlled bythe cycle time ratio. Another embodiment of the invention may providetwo deposition phases and a single etch phase. Another embodiment of theinvention may provide a single deposition phases and two etch phases.Another embodiment of the invention may provide a sequence ofgas-modulated cyclic processes, each cyclic process distinguished by thetotal cycle time, the cycle time ratio, and/or the process conditionsfor the individual phases. These phase conditions include gascompositions, gas flows, RF power, pressure, and/or temperature.

EXAMPLE

A specific example of the invention, as applied to etching a HARCstructure, uses a Exelang HPT dielectric etch system made by LamResearch Corporation™ of Fremont, Calif. for the process chamber 500.The wafers used in this example include a 2.1 μm SiO₂ layer, a patternedphotoresist mask, and a bottom antireflective coating (BARC) between theSiO₂ layer and the photoresist mask. The SiO₂ layer used in this exampleis deposited using plasma enhanced CVD with a tetraethylorthosilicate(TEOS) precursor. The photoresist mask is patterned using 193 nmphotolithography, to produce a contact critical dimension (CD) of 0.16μm or less.

In this example the preparation of the structure (step 306) for thegas-modulated cyclic etch is a BARC etch step. In this example the BARCetch step may one of many known BARC etch steps.

Upon completion of the BARC etch step, the cyclic process is performedin the Exelan HPT dielectric etch system. In this example, which uses anExelan HPT dielectric etch system without modification, the plasma isextinguished twice in each cycle: at the end of the protective layerformation phase 316 and at the end of the etch phase 320. Extinguishingthe plasma allows flexibility in the transition periods. In this case,several seconds were required to stabilize gas flows and pressures, toprepare for the next phase of processing. But with the plasmaextinguished these transition have little or no impact on the processresults. To allow the reignition of the plasma at the start of each etchphase, the initial 2 seconds of the etch phase utilized a higherpressure and lower RF power than the remainder of that phase. Thisstrike portion of the etch phase is considered to be part of the overalletch phase time. In calculating the total processing time, the totalcycle time, and the cycle time ratio, only the plasma-on time periodswere considered. Therefore a nominally 320-second cyclic process in facttook much longer in real time to execute. This inefficient use of timeis the principal shortcoming of this approach. However, this approachprovides the inventive results on an unmodified system.

The protective layer formation phase 316 of the cyclic process 312 isdefined by the following process parameters. The pressure in the waferarea is 120 millitorr, with 500 watts RF power applied at 27 MHz and 500watts applied at 2 MHz. The process gas flows are 500 sccm of Argon and30 sccm of CH₃F. The electrostatic chuck is placed at a temperature of35° C. The backside chuck helium pressure is placed at 15 torr. In thisexample, the deposition gas source 512 would provide the CH₃F, which isnot provided during the etching. The argon may be provided from theadditional gas source 516, since argon is provided during both thedeposition and etching. To initiate the protective layer formationphase, the controller 535 would open the first valve 537 and close thesecond valve 539. The controller would also control the flow of argonfrom the additional gas source. The controller 535 would control thepower and other parameters as specified above.

The etch phase 320 of the cyclic process 312 is defined by the followingprocess parameters. The pressure in the wafer area is 55 millitorr, with1000 watts RF power applied at 27 MHz and 1800 watts applied at 2 MHz.The process gas flows are 270 sccm of Argon, 9 sccm of C₄F₆, and 10 sccmof O₂. The C₄F₆ would be a polymer former gas, which providespolymerization during the etching. The O₂ would be the etching enablergas. Although the fluorine from C₄F₆ is used in etching, the fluorine inthis example requires the presence of oxygen to enable etching. Thechuck is placed at a temperature of 35° C. The backside chuck heliumpressure is placed at 15 torr. In this example, the etchant gas source514 would provide the C₄F₆ and O₂, which are not provided during theprotective layer formation phase, although C₄F₆ without oxygen may beused for deposition. To initiate the etch phase, the controller 535would close the first valve 537 and open the second valve 539. Thecontroller would also control the flow of argon from the additional gassource. The controller 535 would control the power and other parametersas specified above.

In this example, first the BARC etch is performed for 50 seconds (step308). Next, the cyclic process is performed for 320 seconds (step 312),where the plasma off periods are not counted to the time of a phase orthe total cycle time. The duration of the protective layer formationphase 316 is 2 seconds. The duration of the etch phase 320 is 6 seconds,including a 2 second strike condition. Therefore the total cycle time is8 seconds, and the cycle time ratio is 1:3 (protective layer formationphase:etch phase). The cycle is repeated 40 times. After the cyclicprocess is completed (step 312), the photoresist is stripped.

FIGS. 6 and 7 are scanning electron micrographs, showing the results ofetching in a dense array of contacts with nominal critical dimension of0.16 μm for the contact opening. The total etch depth was not enough toreach the silicon nitride stop layer, so these results represent apartial etch process, as is often used to assess etch performance.

Note that the contacts exhibit a small degree of striations, seen asirregularity in the shapes of the circles 604. Without the cyclicprocessing, the striations are typically much worse for this etchapplication.

FIG. 7 is a profile view of etched contacts 704 after PR strip. Notethat the etch profile is fairly vertical, with only slight bowing nearthe top. There is tapering near the bottom of the feature, as usual fora partial etch. This tapering is typically removed when a feature isetched to completion, e.g. when the stop layer is exposed. The etchdepth is about 2 μm. There is no evidence of etch stop, which would beseen as some contacts exhibiting an etch depth much less than othercontacts. Overall these etch results show that the cyclic process iscapable of etching a high-aspect ratio contact with reasonable etchprofile, low striations, and no etch stop. Although this example may notbe fully optimized this example helps to show that the invention mayprovides a superior performance.

A preferred embodiment modifies the process apparatus so that theapparatus is able to provide a preferred process which provides a rapidgas modulation with flow stabilization times of <1 second. In such anembodiment the plasma would remain ignited for the duration of thecyclic process 312, so that there is no plasma off time.

FIG.'S 10A and 10B illustrate a computer system 1000, which is suitablefor implementing a controller 535 used in embodiments of the presentinvention. FIG. 10A shows one possible physical form of the computersystem. Of course, the computer system may have many physical formsranging from an integrated circuit, a printed circuit board, and a smallhandheld device up to a huge super computer. Computer system 1000includes a monitor 1002, a display 1004, a housing 1006, a disk drive1008, a keyboard 1010, and a mouse 1012. Disk 1014 is acomputer-readable medium used to transfer data to and from computersystem 1000.

FIG. 10B is an example of a block diagram for computer system 1000.Attached to system bus 1020 are a wide variety of subsystems.Processor(s) 1022 (also referred to as central processing units, orCPUs) are coupled to storage devices, including memory 1024. Memory 1024includes random access memory (RAM) and read-only memory (ROM). As iswell known in the art, ROM acts to transfer data and instructionsuni-directionally to the CPU and RAM is used typically to transfer dataand instructions in a bi-directional manner. Both of these types ofmemories may include any suitable of the computer-readable mediadescribed below. A fixed disk 1026 is also coupled bi-directionally toCPU 1022; it provides additional data storage capacity and may alsoinclude any of the computer-readable media described below. Fixed disk1026 may be used to store programs, data, and the like and is typicallya secondary storage medium (such as a hard disk) that is slower thanprimary storage. It will be appreciated that the information retainedwithin fixed disk 1026 may, in appropriate cases, be incorporated instandard fashion as virtual memory in memory 1024. Removable disk 1014may take the form of any of the computer-readable media described below.

CPU 1022 is also coupled to a variety of input/output devices, such asdisplay 1004, keyboard 1010, mouse 1012 and speakers 1030. In general,an input/output device may be any of: video displays, track balls, mice,keyboards, microphones, touch-sensitive displays, transducer cardreaders, magnetic or paper tape readers, tablets, styluses, voice orhandwriting recognizers, biometrics readers, or other computers. CPU1022 optionally may be coupled to another computer or telecommunicationsnetwork using network interface 1040. With such a network interface, itis contemplated that the CPU might receive information from the network,or might output information to the network in the course of performingthe above-described method steps. Furthermore, method embodiments of thepresent invention may execute solely upon CPU 1022 or may execute over anetwork such as the Internet in conjunction with a remote CPU thatshares a portion of the processing.

In addition, embodiments of the present invention further relate tocomputer storage products with a computer-readable medium that havecomputer code thereon for performing various computer-implementedoperations. The media and computer code may be those specially designedand constructed for the purposes of the present invention, or they maybe of the kind well known and available to those having skill in thecomputer software arts. Examples of computer-readable media include, butare not limited to: magnetic media such as hard disks, floppy disks, andmagnetic tape; optical media such as CD-ROMs and holographic devices;magneto-optical media such as floptical disks; and hardware devices thatare specially configured to store and execute program code, such asapplication-specific integrated circuits (ASICs), programmable logicdevices (PLDs) and ROM and RAM devices. Examples of computer codeinclude machine code, such as produced by a compiler, and filescontaining higher level code that are executed by a computer using aninterpreter. Computer readable media may also be computer codetransmitted by a computer data signal embodied in a carrier wave andrepresenting a sequence of instructions that are executable by aprocessor.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, modifications andvarious substitute equivalents, which fall within the scope of thisinvention. It should also be noted that there are many alternative waysof implementing the methods and apparatuses of the present invention. Itis therefore intended that the following appended claims be interpretedas including all such alterations, permutations, modifications, andvarious substitute equivalents as fall within the true spirit and scopeof the present invention.

1-16. (canceled)
 17. An apparatus for etching a feature in a layerthrough an etch mask over a substrate, comprising: a process chamber,within which the substrate may be placed; a first gas chemistry sourcefor providing first gas chemistry of a deposition gas chemistry; asecond gas chemistry source for providing a second gas chemistry of areactive etching gas chemistry; a controller controllably connected tothe first gas chemistry source and the second gas chemistry source,wherein the controller comprises computer readable media for performinga gas-modulated cyclic process for more than three cycles, comprising:computer instructions for performing a protective layer forming phaseusing the first gas chemistry with the deposition gas chemistry, whereinthe protective layer forming phase is performed in about 0.0055 to 7seconds for each cycle, comprising; computer instructions for providingthe deposition gas; and computer instructions for forming a plasma fromthe deposition gas; and computer instructions for performing an etchingphase for etching the feature through the etch mask using the second gaschemistry using a reactive etching gas chemistry, where the first gaschemistry is different than the second gas chemistry, wherein theetching phase is performed in about 0.005 to 14 seconds for each cycle,comprising: computer instructions for providing the reactive etchinggas; and computer instructions for forming a plasma from the reactiveetching gas.
 18. The apparatus, as recited in claim 17, furthercomprising: at least one rf power source controlled by the controller;at least one pressure control device controlled by the controller; andat least one temperature control device controlled by the controller,wherein the controller further comprises computer instructions forchanging power from the rf power source during the different phases ofthe modulated cyclic process.
 19. (canceled)
 20. The apparatus, asrecited in claim 18, wherein the computer instructions for performing anetching phase for etching the feature, further comprises computerinstructions for providing an ion bombardment energy of greater than 200electron volts to the substrate.
 21. The apparatus, as recited in claim18, wherein the computer instructions for performing a protective layerforming phase using the first gas chemistry with the deposition gaschemistry performs the protective layer forming phase in 0.25 to 2.5seconds for each cycle.
 22. The apparatus, as recited in claim 21,wherein the computer instructions for performing an etching phase foretching the feature through the etch mask using the second gas chemistryusing a reactive etching gas chemistry performs the etching phase in0.05 to 7 seconds for each cycle.
 23. The apparatus, as recited in claim17, wherein the second gas chemistry contains a polymer former and anetch enabler.
 24. The apparatus, as recited in claim 17, wherein thecomputer readable code for performing the protective layer forming phaseuses a non-directional deposition and the computer readable code forperforming the etching step uses a directional etching.
 25. Theapparatus, as recited in claim 24, wherein the non-directionaldeposition is selected from at least one of chemical vapor depositionand sputtering.
 26. The apparatus, as recited in claim 17, wherein theetch mask is a photoresist mask based upon 193 nm or belowphotolithography.
 27. The apparatus, as recited in claim 17, wherein thecomputer readable media for performing the performing of thegas-modulated cyclic process further comprises computer instructions forperforming a third phase.
 28. The apparatus, as recited in claim 17,wherein the computer readable media for performing the gas-modulatedcyclic process performs the gas-modulated cyclic process for more than20 cycles.
 29. The apparatus, as recited in claim 17, wherein thecomputer readable media for performing the gas-modulated cyclic processperforms the gas-modulated cyclic process for at least 100 cycles. 30.An apparatus for etching a feature in a dielectric layer through an etchmask over a substrate, comprising: a process chamber, within which thesubstrate may be placed; a first gas chemistry source for providingfirst gas chemistry of a deposition gas chemistry; a second gaschemistry source for providing a second gas chemistry of a reactiveetching gas chemistry; a controller controllably connected to the firstgas chemistry source and the second gas chemistry source, wherein thecontroller comprises computer readable media for performing agas-modulated cyclic process for more than twenty cycles, comprising:computer instructions for performing a protective layer forming phaseusing the first gas chemistry with the deposition gas chemistry, whereinthe protective layer forming phase is performed in about 0.25 to 2.5seconds for each cycle, comprising; computer instructions for providingthe deposition gas; and computer instructions for forming a plasma fromthe deposition gas; and computer instructions for performing an etchingphase for etching the feature into the dielectric layer through the etchmask using the second gas chemistry using a reactive etching gaschemistry, where the first gas chemistry is different than the secondgas chemistry, wherein the etching phase is performed in about 0.05 to 7seconds for each cycle, comprising: computer instructions for providingthe reactive etching gas comprising a polymer former and an etchenabler; computer instructions for forming a plasma from the reactiveetching gas; and computer instructions for providing an ion bombardmentenergy of greater than 200 electron volts to the substrate.
 31. Theapparatus, as recited in claim 30, further comprising: at least one rfpower source controlled by the controller; at least one pressure controldevice controlled by the controller; and at least one temperaturecontrol device controlled by the controller, wherein the controllerfurther comprises computer instructions for changing power from the rfpower source during the different phases of the modulated cyclicprocess.
 32. The apparatus, as recited in claim 30, the computerreadable code for performing the protective layer forming phase uses anon-directional deposition and the computer readable code for performingthe etching step uses a directional etching.
 33. The apparatus, asrecited in claim 32, wherein the non-directional deposition is selectedfrom at least one of chemical vapor deposition and sputtering.
 34. Theapparatus, as recited in claim 30, wherein the etch mask is aphotoresist mask based upon 193 nm or below photolithography.
 35. Theapparatus, as recited in claim 30, wherein the computer readable mediafor performing the performing of the gas-modulated cyclic processfurther comprises computer instructions for performing a third phase.36. The apparatus, as recited in claim 30, wherein the computer readablemedia for performing the gas-modulated cyclic process performs thegas-modulated cyclic process for at least 100 cycles.
 37. An apparatusfor etching a feature in a dielectric layer through an etch mask over asubstrate, comprising: a process chamber, within which the substrate maybe placed; a first etch gas chemistry source for providing first etchgas chemistry; a second etch gas chemistry source for providing a secondetch gas chemistry; a controller controllably connected to the firstetch gas chemistry source and the second etch gas chemistry source,wherein the controller comprises computer readable media for performinga gas-modulated cyclic process for at least 3 cycles, comprising:computer instructions for performing a first etching phase, wherein thefirst etching phase is performed in about 0.0055 to 14 seconds for eachcycle, comprising; computer instructions for providing a first etch gas;and computer instructions for forming a plasma from the first etch gas;and computer instructions for performing a second etching phase, whereinthe second etching phase is performed in about 0.0055 to 14 seconds foreach cycle, comprising; computer instructions for providing a secondetch gas, wherein the first etch gas is different than the second etchgas; and computer instructions for forming a plasma from the second etchgas.